import RPi.GPIO as GPIO
import time
GPIO.setwarnings(False) 
GPIO.cleanup()
GPIO.setmode(GPIO.BCM)
GPIO.setup(20,GPIO.OUT)
GPIO.setup(21,GPIO.OUT)
while True:
   GPIO.output(20, GPIO.HIGH)
   time.sleep(0.1)
   GPIO.output(20, GPIO.LOW)
   time.sleep(0.1)
   GPIO.output(21, GPIO.HIGH)
   time.sleep(0.1)
   GPIO.output(21, GPIO.LOW)
   time.sleep(0.1)